The following invention relates generally to a system and device for replacing damaged screw threads in an object, and in particular to a system and device for replacing damaged screw threads which will replace the threads with a permanently installed insert, the insert also provides a seal between the insert and the object to be repaired.
When internal screw threads cut into an object become damaged, they can sometimes be repaired by chasing the damaged thread with a tap to restore the thread shape. However, if the thread is damaged to such an extent that chasing with a tap will not restore its function, the thread must be replaced. This can be done by boring out the original threads with a drill larger than the major diameter of the thread and rethreading the hole with a larger diameter thread. While this method will provide a usable threaded hole, it will require a fastener of a different size than the original. In an assembly which must be dissembled and reassembled periodically, this method requires that tools with different head sizes are needed. This is, at the very least inconvenient and may result in difficulty for those reassembling the device.
In order to replace the damaged thread with the same thread as the original assembly, it is necessary to bore the damaged threads out and replace the original threads with a thread-insert which can be threaded into the larger bored out and threaded hole and which has internal threads the same as the original threads. Such thread inserts are available, however the external threads of the thread-inserts are generally of conventional helical design. A conventional thread-insert has a tendency to become loose when the machine screw is removed for disassembly or, in some cases, the thread-insert will unscrew from the object when removal of the attaching screw is attempted thus complicating the disassembly process. In addition, if the attaching screw must provide a sealed engagement with the object, a conventional thread-insert will not usually provide a seal between its external threads and the wall of the object.
The following prior art reflects the state of the art of which applicant is aware and is included herewith to discharge applicant""s acknowledged duty to disclose relevant prior art. It is stipulated, however, that none teaches or render obvious the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
The present invention has as its objective to provide thread-insert which will avoid the disadvantages noted above.
The present invention overcomes the disadvantages of the prior art noted above by first, providing a thread-insert which is fastened into a hole in the object using a thread design on the external surface of the insert and a matching thread formed in the bored out hole. The thread-insert has upwardly slanted thread surfaces that angle upward toward the head which lock the insert securely into the replacement hole of the object. The effect of these threads is to provide a radially inward clamping force as the insert is tightened, due to a clamping reaction of the threads vis-a-vis another part of the insert against the object receiving the insert. Secondly, the thread-insert has an internal thread preferably adapted to receive a desired standard threaded fastener. Thirdly, the thread-insert preferably includes a drive head that can include any of a variety of torque-receiving configurations. For instance, the drive head can have multiple facets dimensioned to be addressed by facets of a wrench. In addition, slots may be formed complementary to a slotted screw driver or other similar structures. Thus, the drive head receives torque and causes the thread repair insert to rotate about a central, long axis thereof. Below the drive head, the insert preferably includes a neck.
The thread-insert is provided with a pocket interposed between the neck and the upper surface of the upper most thread on the thread-insert. When the insert is threaded completely into the thread of the bored out hole, the insert deforms the metal of the thread from the object, forcing it into the pocket forming a tight seal between the insert and the wall of the object.
Accordingly, it is a primary object of the present invention to provide a thread-insert that upon tightening forms a tight-seal between the insert and the wall of an object.
A further object of the present invention is to provide a thread-insert which permits the same thread as the original undamaged threads so as to avoid the complexities of different size fasteners needed to assemble and disassemble an object or objects.
Another further object of the present invention is to provide a thread-insert that avoids the tendency to become loose when disassembly is required.
Another further object of the present invention is to provide a thread-insert that avoids the tendency to become loose when disassembly is required by providing exterior threads that are upwardly slanted thread surfaces that angle upward toward the head of the thread-insert and lock the insert securely into the replacement hole of the object.
A further of object of the present invention is to provide a thread-insert that has a pocket formed between the neck and the upper surface of the upper most thread wherein when the thread-insert is tightened, the metal of the object that constitutes the matching threads flows into the pocket thus creating a seal between the insert and the wall of the object.
Another further object of the present invention is to provide a thread-insert which includes having exterior threads and interior threads disposed thereon.
Another further object of the present invention is to provide a thread-insert which includes a drive head which is driveable by a commonly available torque-applying instrumentality.
Another further object of the present invention is to provide a thread-insert whereby the exterior threads preclude the thread-insert from disengaging from the threaded hole.
Another further object of the present invention is to provide a thread-insert which is designed to enter a complementary formed hole a finite distance.
Another further object of the present invention is to provide a thread-insert wherein the exterior threads are slightly spaced from each other and maintain a minimum thickness between a root and a crest thereof, providing a durable thread.
Another further object of the present invention is to provide a thread-insert which is simple and inexpensive to manufacture and yet durable in construction.
Viewed from a first vantage point it is a feature of the present invention to provide a method for providing a seal between a thread-insert and an object the thread-insert is inserted therein, comprising the steps of: boring a hole; cutting the top of the hole to match the shape of the thread-insert; tapping matching threads in the hole; threading the thread-insert into the hole until seated; and further threading the thread-insert into the hole to cause metal flow.
Viewed from a second vantage point it is a feature of the present invention to provide a thread-insert that forms a seal between itself and an object within which it is threaded. The thread-insert has a threaded shaft extending from a drive head along a central axis to a distal end; at least one of said shaft threads includes a crest defining a major diameter of said threaded shaft, a root defining a minor diameter of the threaded shaft, and an upper surface extending from a bottom edge of said root to an upper edge of the crest, wherein said upper surface having a portion thereof extending toward the crest at an angle greater that zero from a reference plane perpendicular to the central axis of said threaded shaft; and a pocket interposed between the upper most thread of the threaded shaft and the lower portion of the head.
Viewed from a third vantage point it is a feature of the present invention to provide a pocket portion of a thread-insert interposed between an upper most thread and a neck portion located under a drive head of the thread-insert, wherein the upper most thread and said neck portion are in a spaced relationship with a common central axis running therethrough, the neck being formed from an outer cylindrical surface of a diameter d1. The pocket portion is defined by surfaces comprising: a relief surface that intersects the neck with the diameter of d1 at an acute angle and intersects an inner cylindrical surface with a diameter of d2, at the acute angle, wherein d1 is greater than d2 and the cylindrical surfaces are parallel to said common central axis of the thread-insert and concentric to each other; the inner cylindrical surface; and an upper surface at an angle relative to the common central axis of the upper most thread.
These and other objects will be made manifest when considering the following detailed specification when taken in conjunction with the appended drawing figures.